This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/IB99/02021 which has an International filing date of Dec. 17, 1999, which designated the United States of America and was published in English.
The present invention relates to an apparatus for heating chemical reaction mixtures. In particular, the present invention relates to an apparatus applying one or more semiconductor based microwave generators making the apparatus suitable for parallel processing of chemical reaction mixtures. The invention further relates to methods for performing chemical reactions, e.g. methods for heating a plurality of samples simultaneously or sequentially, methods for monitoring a microwave heated chemical reaction and methods where the optimum conditions with respect to frequency and applied power can be determined.
One of the major obstacles for an organic chemist today is the time consuming search for efficient routes in organic synthesis. As an example, the average performance some ten years ago in the pharmaceutical industry was around 25-50 complete substances per chemist per year resulting in an equal amount of new chemical entities as potential new drug candidates. Today the figure is several 100""s per year and will soon be expected to be in the region of 1000""s per year.
Thus, the challenges for the pharmaceutical industries and the organic chemist include identification of ways of reducing time in drug development, identification of ways of creating chemical diversity, development of new synthesis routes and maybe reintroduction of old xe2x80x9cimpossiblexe2x80x9d synthetic routes. Also, it is a constant challenge to reach classes of totally new chemical entities.
As it will be apparent from the following, microwaves assisted chemistry offers a way to circumvent at least some of the above-mentioned problems, namely
speeding up the reaction time with several orders of magnitudes,
improving the yield of chemical reactions,
offering higher purity of the resulting product due to rapid heating and thereby avoiding impurities from side reactions, and
performing reactions which are not possible with conventional thermal heating techniques.
Microwave assisted chemistry has been used for many years. However, the apparatuses and methods have to a great extent been based on conventional domestic microwave ovens. Domestic microwave ovens have a multimode cavity and the energy is applied at a fixed frequency at 915 MHz or 2450 MHz (depending on country). The use of single mode cavities have also been reported, see e.g. U.S. Pat. No. 5,393,492 and U.S. Pat. No. 4,681,740.
The market for microwave generators is totally dominated by magnetrons. In some situations travelling wave tubes (TWT) are used to amplify a microwave signal. There are several disadvantages related to the conventional apparatuses. Some of these will be listed in the following:
It is a disadvantage that the energy distribution in conventional microwave ovens is non-uniform. This leads to a varying temperature in the sample depending on the position of the sample in the oven. Furthermore, the non-uniform energy distribution makes it difficult to obtain reproducible results. This effect is especially noticeable if an array of sample holders such as a microtiter plate (e.g. with 96 wells) is used. Rotation of the sample in the oven does not significantly improve the reproducibility.
In conventional systems the power provided to each sample in an array of samples can only be calculate as an average power per sample by dividing the measured input power with the total number of samples. Due to the non-uniform energy distribution in the cavity this calculation will only provide a rough estimate of the applied power to each sample.
One way of controlling the reaction is to monitor pressure and temperature in all individual wells. This may give information of the conditions in a specified well during a particular run. Changing the position will give a different result leading to poor reproducibility. An alternative way of trying to obtain a uniform energy distribution is to place a large load in the cavity in order to absorb energy more uniformly.
Single mode cavity resonators offer a possibility of high efficiency and controlled heating patterns in small loads. However, the dielectric properties of the load often change considerably with temperature, resulting in very large variations in power absorption since an essentially constant frequency microwave generator is used. Hence, the process becomes difficult to predict.
A further disadvantage of conventional system relates to the fact that magnetrons usually only provide a fixed frequency or a minor adjustment around the center frequency of the magnetron. Furthermore, magnetrons have an unpredictable behaviour and are extremely temperature sensitive, especially when the efficiency decreases, towards the end of its xe2x80x9clifexe2x80x9d.
TWT""s have be used as variable frequency amplifiers. However,TWT""s are rather expensive and often very complicated to use. Furthermore,TWT""s require warm-up time before start meaning that TWT""s cannot rapidly be switched on and off. In addition, wear out of TWT""s is associated with high maintenance costs.
Both magnetrons and TWT""s require a high voltage power supply, which is a disadvantage in view of complications and the risk.
In U.S. Pat. No. 5,521,360 a variable frequency heating apparatus for providing microwaves into a furnace cavity is described. The apparatus comprises a voltage controlled microwave generator, a voltage controlled pre-amplifier and a power amplifier. The power amplifier may be a TWT. The TWT is operationally connected to the furnace cavity. The power delivered to the furnace is determined by measuring the power reflected from the furnace using a power meter. Upon placing a sample in the cavity furnace, power may be coupled to the sample causing the temperature of the sample to change.
The system described in U.S. Pat. No. 5,521,360 suffers from the above-mentioned disadvantages relating to e.g. TWT""s.
It is a further disadvantage of the apparatus described in U.S. Pat. No. 5,521,360 that it is restricted to be used with only one cavity furnace, i.e. parallel heating of a plurality of samples using different heating parameters is not possible.
It is another object of the present invention to provide an apparatus comprising a first semi-conductor based electromagnetic generator, and a first applicator for holding a sample, which apparatus are capable of performing a controlled heating of the sample.
It is another object of the present invention to provide an apparatus capable of performing parallel processing of many samples, with individually settings of process parameters such as frequency, power, temperature, pressure etc.
It is a further object of the present invention to provide an apparatus capable of monitoring many samples in parallel, with individually monitoring of process parameters such as frequency, power, temperature, pressure etc.
It is a still further object of the present invention to provide an apparatus capable of controlling many samples in parallel, with individually adjustments of process parameters such as frequency, power, temperature, pressure etc.
It is a still further object of the present invention to provide an apparatus in which samples can be evenly heated by using various applicators.
It is a still further object of the present invention to provide an apparatus in which the frequency of the applied energy can be varied.
It is a still further object of the present invention to provide an apparatus in which it is possible to evaluate and separate thermal and chemical effects on the electromagnetic absorption capability and behaviour of the sample.
It is a still further object of the present invention to provide an apparatus in which it is possible to measure the temperature in the reaction vessel by monitoring the change in resonance frequency of a second material introduced into the reaction chamber. This material could be a crystal, semiconductor or any other solid state material with a temperature dependent resonance frequency.
The above-mentioned objects are complied with by providing in a first aspect an apparatus for providing electromagnetic radiation to a first applicator, said apparatus comprising:
a) a first generating means for generating electromagnetic radiation,
b) a first amplifying means for amplifying the generated electromagnetic radiation,
c) means for guiding the amplified electromagnetic radiation to the first applicator, and
d) means for controlling the first generating means and the first amplifying means,
wherein the generated electromagnetic radiation comprises a plurality of frequencies, and wherein the first generating means and the first amplifying means are essentially constituted by semiconductor components.
By essentially constituted by semiconductor components is meant that the components generating the electromagnetic radiationxe2x80x94such as the required power transistorsxe2x80x94are semi-conductor based power transistors.
In the present context, guiding means should be interpreted as any means capable of guiding electromagnetic radiation such as metallic channels or cables, such as coaxial cables or wave-guides. The guiding means may also comprise active and/or passive components such as couplers, dividers, splitters, combiners, isolators, power meters, artificial loads, spectrum analysers etc.
In order to perform parallel processing of a plurality samples the apparatus may comprise a second applicator and suitable guiding means for guiding at least part of the amplified electromagnetic radiation to the second applicator. Generally it may be favourable to be able to provide electromagnetic radiation with different frequencies to the first and second applicator. Therefore, the apparatus may comprise a second generating means for generating electromagnetic radiation at a plurality of frequencies and a second amplifying means for amplifying the electromagnetic radiation generated by the second generating means. In order to provide electromagnetic radiation at a plurality of frequencies the second generating means and the second amplifying means are preferably constituted by semiconductor components, such as semiconductor based power transistors. Examples of such power transistors are silicon-carbide power transistors. It is evident that the same type of transistors may be used in first generating means and the first amplifying means.
To increase flexibility of the apparatus, the guiding means may comprise means for guiding the electromagnetic radiation amplified by the second amplifying means to the second applicator. In addition, the guiding means may further comprise means for guiding at least part of the electromagnetic radiation amplified by the second amplifying means to the first applicator.
Also, in order to further increase flexibility of the apparatus the guiding means may comprise means for switching the electromagnetic radiation amplified by the first amplifying means between the first and second applicator. Furthermore, the guiding means may comprise means for switching the electromagnetic radiation amplified by the second amplifying means between the first and second applicator.
The first and second applicators may be of various types. Preferable, the first and second applicators are selected from the group consisting of quasistatic, near field, surface field, single mode cavity and multi mode cavity applicators.
The frequency of the electromagnetic radiation generated by the first and second generating means may vary according to a first and second control signal, respectively. These first and second control signals may be provided by the control means. Similarly, the amplification of the first and second amplifying means may vary in accordance with a first and a second control signal, respectively. Also these signals may be provided by the control means. The control means may comprise a general purpose computer. Such a general purpose computer may form part of a neural network.
The frequency of the electromagnetic radiation generated by the first and second generating means is within the range 300 MHz-300 GHz, such as within the range 0,5-3 GHz or within the range 50-100 GHz.
In a second aspect, the present invention relates to a method for performing a plurality of chemical reactions simultaneously or sequentially, said method comprising the steps of:
a) providing a first sample into a first applicator,
b) providing a second sample into a second applicator, and
c) applying electromagnetic radiation to the first and second samples simultaneously or sequentially for a predetermined period of time, said electromagnetic radiation having a frequency in the range of 300 MHz-300 GHz.
The electromagnetic radiation may be provided specifically and independently to each of the samples. In addition, the applied electromagnetic radiation may comprise one or more pulses. The samples may be collected in sets comprising at least two holders. The sample itself may be a PCR mixture. During exposure of a sample the electromagnetic radiation may be applied in cycles of at least two steps where the sample is cooled at least during part of each cycle.
Preferably, the electromagnetic radiation is provided using an apparatus according to the first aspect of the present invention.
In a third aspect, the present invention relates to a method for performing a chemical reaction, said method comprising the steps of:
a) providing a sample in an applicator,
b) applying electromagnetic radiation to the sample for a first predetermined period of time at a first level of power and varying the frequency of the electromagnetic radiation between two predetermined values and with a predetermined resolution, and determining a reflection factor of electromagnetic radiation from the sample at at least some (two) of the frequencies covered by the range of the two predetermined values by determining the level of a feed-back signal, thereby obtaining a first set of reflection factors,
c) changing the physical and/or chemical properties of the sample,
d) applying electromagnetic radiation to the applicator at a second level of power and varying the frequency of the electromagnetic radiation between two predetermined values and with a predetermined resolution, the range defined by the predetermined values being included in the range defined by the predetermined values in step b), and determining a reflection factor of electromagnetic radiation from the sample at at least some (two) of the frequencies covered by the range of the two predetermined values by determining the level of the feed-back signal, thereby obtaining a second set of reflection factors, and
e) repeating step c) and d) until the difference in reflection factors calculated as the mathematical difference (subtraction) between the frequencies associated with the first and second set of reflection factors is within a predetermined range.
Step c) may comprise applying electromagnetic radiation for heating the sample. Alternatively or in addition, the sample may also be cooled and/or a reagent may be added to the sample. Also, if the difference in reflection factors is within the predetermined range after the first execution of step c) and d), step e) will off course no longer apply. Furthermore, if the difference is close to being within the predetermined range, it might not be economical to perform step e), and it may be omitted.
In a fourth aspect, the present invention relates to a method for performing a chemical reaction, said method comprising the steps of:
a) providing a sample in an applicator,
b) applying electromagnetic radiation to the sample, the electromagnetic radiation having a starting frequency,
c) varying the frequency of the applied electromagnetic radiation between two predetermined values and with a predetermined resolution,
d) determining a reflection factor of electromagnetic radiation from the sample by determining a level of a feed-back signal during at least part of the varying of the frequency of the electromagnetic radiation, and
e) determining, from the level of the feed-back signal, the frequency of the electromagnetic radiation where the reflection factor is within a predetermined range.
In a fifth aspect, the present invention relates to a method for performing a chemical reaction, said method comprising the steps of:
a) providing a sample in an applicator,
b) applying electromagnetic radiation to the sample, the electromagnetic radiation having a starting frequency,
c) varying the frequency of the electromagnetic radiation incrementally around the starting frequency,
d) determining a reflection factor of electromagnetic radiation from the sample by determining a level of a feed-back signal at the starting frequency, at a frequency incrementally lower than the starting frequency and at a frequency incrementally higher than the starting frequency,
e) repeating step b) to d) until the reflection factor is minimum.
In a sixth aspect, the present invention relates to a method for performing a chemical reaction, said method comprising the steps of:
a) providing a sample in an applicator,
b) applying electromagnetic radiation to the sample, the electromagnetic radiation having a starting frequency,
c) varying the frequency of the electromagnetic radiation incrementally around the starting frequency,
d) determining a reflection factor of electromagnetic radiation from the sample by determining a level of a feed-back signal at the starting frequency, at a frequency incrementally lower than the starting frequency and a frequency incrementally higher than the starting frequency,
e) comparing the determined reflection factor with a predetermined reflection factor,
f) adjusting the starting frequency to a frequency so that the determined reflection factor is within a predetermined range around the predetermined reflection factor, and
g) repeating step c) to f) as often as desirable.
The starting frequency may be in the range of 300 MHz-300 GHz. The predetermined values between which the frequency of the electromagnetic radiation may be varied are in the range of 300 MHz-300 GHz, such as within the range 0,5-3 GHz or within the range 50-100 GHz. Preferably, the reactions according the third, fourth, fifth and sixth are performed using an apparatus according to first aspect of the present invention.
In a seventh aspect, the present invention relates to a method for performing a chemical reaction, said method comprising the steps of:
a) providing a sample in an applicator,
b) applying electromagnetic radiation to the sample in form of a first pulse with a predetermined shape and characterising a reflected pulse from the applicator by performing a mathematical operation so as to obtain a first reflected spectrum,
c) changing the physical and/or chemical properties of the sample,
d) applying electromagnetic radiation to the sample in form of a second pulse with a predetermined shape and characterising a reflected pulse from the applicator by performing a mathematical operation so as to obtain a second reflected spectrum,
e) repeating step c) and d) until the difference between the first and second reflected spectra calculated as the mathematical difference (subtraction) between the first and second spectra is within a predetermined range.
If the difference in reflection factors is within the predetermined range after the first execution of step c) and d), step e) will off course no longer apply. Furthermore, if the difference is close to being within the predetermined range, it might not be economical to perform step e), and it may be omitted. Preferably, the mathematical operation for obtaining the first and second reflection spectra comprises Fourier Transformation but alternative operations may also be applicable. The method according to the seventh aspect of the present invention may be performed using an apparatus according the first aspect of the present invention.
In a eight aspect, the present invention relates to the use of an apparatus according to the first aspect of the present invention for heating at least one sample comprising at least one organic compound. Each of the samples may further comprise one or more reagents and optionally a catalyst. Preferable, the apparatus according the first aspect of the present invention is configured to heat two or more reaction mixtures, such as PCR mixtures, simultaneously or sequentially or intermittently.
The frequency of the electromagnetic radiation, the level of irradiated power and the period of applying the electromagnetic radiation is determined by pre-set values for the chemical reaction in question, such pre-set values being stored in a storage means associated with the control means. Corresponding data of frequency and reflection factor may be stored in a memory for further processing. Further processing may be performed in a neural network.
In a ninth aspect, the present invention relates to a kit for chemically reacting chemical species with a reagent optionally under the action of a catalyst, wherein the chemical reaction is performed in an apparatus according to the first aspect of the present invention, said kit comprising:
a) a sample holder comprising at least one of the reagent and the optional catalyst,
b) an electronic storage means comprising data concerning the chemical reaction between the chemical species and the reagent under the optional action of the catalyst, said electronic storage means and apparatus being adapted for retrieving the data from the storage means and processing said data so as to control the application of an electromagnetic radiation to said sample holder.